Method for operating an internal combustion engine, in particular, of a motor vehicle

ABSTRACT

An internal combustion engine for a motor vehicle. In the internal combustion engine, fuel is injected directly into a combustion chamber and is burned during an intake phase in a first mode of operation and during a compression phase in a second mode of operation. Exhaust gas formed by combustion may be sent to a catalytic converter. A controller may cause additional fuel to be injected following combustion in the second mode of operation. The controller may also cause the temperature of the exhaust gas to be measured in or downstream from the catalytic converter and compared with a threshold value.

FIELD OF THE INVENTION

The present invention relates to a method for operating an internalcombustion engine of a motor vehicle, in which fuel is injected directlyinto a combustion chamber and burned during an intake phase in a firstmode of operation and during a compression phase in a second mode ofoperation, and in which exhaust gas formed by combustion is sent to acatalytic converter. The present invention also relates to a controllerfor an internal combustion engine of a motor vehicle and to an internalcombustion engine for a motor vehicle.

BACKGROUND INFORMATION

Such a method, such a controller and such an internal combustion engineare conventional in direct gasoline injection, for example, where fuelis injected into the combustion chamber of the internal combustionengine during the intake phase in homogenous operation or during thecompression phase in stratified charge operation. Homogeneous operationis provided for full-load operation of the internal combustion engine,while stratified charge operation is suitable for idling and partialload operation. Such a direct injection internal combustion engine isswitched between these modes of operation as a function of the requiredtorque, for example. For implementation of stratified charge operationit is necessary to have a catalytic converter with which the nitrogenoxides formed may be stored temporarily in a storage catalytic converterso that they may be reduced during a subsequent homogeneous operation.The storage catalytic converter is loaded with nitrogen oxides instratified charge operation and is unloaded again in homogeneousoperation. This loading and unloading as well as the associatedconversion of nitrogen oxides to nitrogen and oxygen result in aging ofthe catalytic converter.

SUMMARY OF THE INVENTION

It is an object of the present invention to create a method of operatinga storage catalytic converter of an internal combustion engine withwhich the aging of the storage catalytic converter is detectable.

The exhaust gas generated in the internal combustion engine containspollutants which are converted in the catalytic converter. These includeunburned hydrocarbons and carbon monoxide. Conversion of thesepollutants results in an increase in temperature of the resultingexhaust gases. However, this increase in temperature is less in the caseof an aged catalytic converter due to its reduced conversion capacity.It is thus fundamentally possible to use the resulting increase intemperature as a measure of the aging of the catalytic converter.

This temperature increase occurs even without the additionally injectedfuel. In this case, however, the temperature increase is so slight,e.g., in the case of an aged catalytic converter, that it may no longerallow reliable determination of aging of the catalytic converter.

An additional conversion and thus also an additional increase intemperature of the exhaust gas is achieved by injection of additionalfuel. This may allow a reliable and certain determination of the agingstatus of the catalytic converter. In an example embodiment of thepresent invention, a temperature increase is measured and compared witha temperature increase measured with a new catalytic converter, and thedifference is compared with an upper limit value. It is thus readilypossible to detect an aged catalytic converter.

In a similar manner, a temperature increase is measured and comparedwith a modeled temperature increase, and the difference is compared withan upper limit value.

In another example embodiment of the present invention, a maximumtemperature is measured and compared with a lower threshold value. Thisis an option for implementation of the present invention that may beexecuted especially easily and rapidly.

It may be advantageous if the additional fuel injected is not ignited.This guarantees that the unburned fuel in the form of unburnedhydrocarbons and carbon monoxide will enter the exhaust pipe and thecatalytic converter and result in an elevated temperature there.

Implementation of the method according to the present invention in theform of a control element which is provided for a controller of aninternal combustion engine in a motor vehicle is especially important. Aprogram capable of running on a computer, e.g., on a microprocessor, andsuitable for execution of the method according to the present inventionis stored on this control element. Thus in this case, the presentinvention is implemented by a program stored on this control element, sothat this control element equipped with the program constitutes thepresent invention in the same manner as the method for whose executionthe program is suitable. An electric memory medium such as a read-onlymemory or a flash memory may be used as the control element.

Additional features, possible applications and advantages of the presentinvention are derived from the following description of exampleembodiments of the present invention which are illustrated in thefigures in the drawing. All the features illustrated or described here,either alone or in any desired combination, constitute the object of thepresent invention, regardless of how they are combined in the patentclaims or their reference back to preceding claims and independently ofhow they are formulated in the description or illustrated in thedrawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of an example embodiment of an engineaccording to the present invention.

FIG. 2 shows a schematic diagram of temperature increases with thecombustion engine in FIG. 1.

DETAILED DESCRIPTION

FIG. 1 shows an internal combustion engine 1 of a motor vehicle in whicha piston 2 is movable back and forth in a cylinder 3. Cylinder 3 isequipped with a combustion chamber 4 delimited by piston 2, an intakevalve 5 and an exhaust valve 6. An intake manifold 7 is connected tointake valve 5, and an exhaust pipe 8 is connected to exhaust valve 6.

A fuel injector 9 and a spark plug 10 protrude into combustion chamber 4in the area of intake valve 5 and exhaust valve 6. Fuel may be injectedinto combustion chamber 4 through intake valve 9. Fuel in combustionchamber 4 may be ignited with spark plug 10.

A rotatable throttle valve 11 through which air may be supplied tointake manifold 7 is accommodated in intake manifold 7. The amount ofair supplied depends on the angular setting of throttle valve 11. Acatalytic converter 12 is accommodated in exhaust pipe 8 to purify theexhaust gas formed by combustion of fuel.

Catalytic converter 12 in the present example embodiment is a three-waycatalytic converter 12′ which is combined with a storage catalyticconverter 12″. It is self-evident that other types and/or combinationsof catalytic converters are also conceivable. For example, preliminarycatalytic converters and main catalytic converters and the like may alsobe provided. The catalytic converter 12 is suitable for treatment andfor conversion of the pollutants of the exhaust gas generated byinternal combustion engine 1.

A temperature sensor 13 is included in catalytic converter 12.Alternatively or additionally, a temperature sensor 14 is included inthe exhaust pipe directly downstream from catalytic converter 12.

A controller 18 receives input signals 19 representing operatingvariables of internal combustion engine 1 measured by sensors.Controller 18 generates output signals 20 with which the performance ofinternal combustion engine 1 may be influenced via actuators. Amongother things, controller 18 is provided for controlling and/orregulating the operating variables of internal combustion engine 1. Tothis end, controller 18 is equipped with a microprocessor which includesa program suitable for execution of this control and/or regulationstored in a memory medium, e.g., in a flash memory.

In a first mode of operation, referred to as homogeneous operation ofinternal combustion engine 1, throttle valve 11 is partially opened orclosed as a function of the desired torque. Fuel is injected by injector9 into combustion chamber 4 during an intake phase produced by piston 2.Turbulence is created in the injected fuel due to the simultaneous airintake through throttle valve 11, and thus fuel is distributed uniformlyin combustion chamber 4. Then the fuel/air mixture is compressed duringthe compression phase and ignited by spark plug 10. Expansion of ignitedfuel drives piston 2. The resulting torque in homogeneous operationdepends on the setting of throttle valve 11, among other things. Fromthe standpoint of low emissions, the fuel/air mixture is set as closelyas possible to a lambda value of one.

In a second mode of operation, referred to as stratified chargeoperation of internal combustion engine 1, throttle valve 11 is wideopen. Fuel is injected into combustion chamber 4 by injector 9 during acompression phase produced by piston 2, namely locally in the immediatevicinity of spark plug 10 and chronologically at a suitable intervalbefore the ignition time. Then the fuel is ignited with the help ofspark plug 10, so that piston 2 is driven by the expansion of theignited fuel in the following working phase. The resulting torque instratified charge operation depends largely on the fuel mass injected.Stratified charge operation is provided for idling operation and partialload operation of internal combustion engine 1.

Storage catalytic converter 12″ of catalytic converter 12 is loaded withnitrogen oxides during stratified charge operation. In a subsequenthomogeneous operation, storage catalytic converter 12″ is unloadedagain, and the nitrogen oxides are reduced by three-way catalyticconverter 12′.

Storage catalytic converter 12″ takes up sulfur over a period of timeduring its continuous loading and unloading of nitrogen oxides. Thisresults in a diminished storage capacity of storage catalytic converter12″, which is referred to below as aging. The continuous conversion ofexhaust gases to nitrogen and oxygen, among other things, in three-waycatalytic converter 12′ results in a diminished conversion capacity andthus to aging.

The conversion of the exhaust gases in three-way catalytic converter 12′is an exothermic reaction in which heat is generated. This results in anincrease in the temperature of the exhaust gases flowing throughcatalytic converter 12. This temperature increase is measured bytemperature sensor 13 and/or by temperature sensor 14. At the same time,there is also an increase in the temperature of catalytic converter 12itself due to the exothermic reaction and this is alternatively oradditionally measured by temperature sensor 13 and optionally also bytemperature sensor 14.

However, the increase in temperature produced by the exothermic reactionis not sufficient to be detected reliably.

For this reason, an additional injection of fuel into combustion chamber4 following combustion is triggered by controller 18 in stratifiedcharge operation of internal combustion engine 1. However, this fuel isnot ignited. Therefore, unburned fuel enters exhaust pipe 8 andcatalytic converter 12. Due to the oxygen present there and the hightemperatures prevailing there, the fuel in exhaust pipe 8 and incatalytic converter 12 reacts with the oxygen. This results in anincrease in temperature of the exhaust gas in exhaust pipe 8 and incatalytic converter 12.

The exhaust gas present in exhaust pipe 8 and having an elevatedtemperature goes to catalytic converter 12, where there is anotherincrease in temperature due to the conversion of the exhaust gasresulting from the additional injection. On the whole, this results in agreater temperature increase due to the conversion of the exhaust gas bycatalytic converter 12.

In addition, the higher temperature of the exhaust gas enteringcatalytic converter 12 also results in a greater temperature increase inthe exhaust gas in catalytic converter 12 due to the conversion.

Due to the additional injection of fuel following combustion instratified charge operation, a greater increase in temperature of theexhaust gas is thus achieved due to the conversion of same in catalyticconverter 12.

Due to the aging of three-way catalytic converter 12′, the ability toconvert exhaust gases in three-way catalytic converter 12′ declines.This results in a diminished reaction of fuel and oxygen in catalyticconverter 12 and thus to a reduction in the resulting rise intemperature. The lower ability to convert results in a reduction in theexothermic reaction produced by the conversion and thus to a reductionin the resulting temperature increase.

Controller 18 monitors the temperature increase measured instantaneouslyduring operation of internal combustion engine 1. This may occur bycomparing the instantaneous temperature increase with a temperatureincrease measured with a new three-way catalytic converter 12′ or a newcatalytic converter 12. Alternatively or additionally, the instantaneoustemperature increase may be compared with a temperature increasemeasured with a defective three-way catalytic converter 12′ or catalyticconverter 12. Alternatively or additionally, this may also occur bycomparing the instantaneous temperature increase with a modeledtemperature increase.

In a comparison with a new catalytic converter 12, the differencebetween the temperature increase measured instantaneously and thetemperature increase of new catalytic converter 12 becomes progressivelygreater. When the difference between the instantaneous temperatureincrease and the temperature increase of new catalytic converter 12exceeds an upper threshold value, controller 18 deduces that catalyticconverter 12 has now reached a stage of aging which is no longeracceptable from the standpoint of adequate exhaust purification.Controller 8 then generates a signal, for example, which may beperceived by the driver or by a workshop and indicates that catalyticconverter 12 should be replaced.

In a comparison with a defective catalytic converter 12, the differencebetween the temperature increase measured instantaneously and thetemperature increase of defective catalytic converter 12 becomesprogressively smaller, so that the difference is compared with arespective lower threshold value which, when reached, indicates thatcatalytic converter 12 should be replaced.

When using the modeled temperature increase, the difference incomparison with the instantaneous temperature increase becomesprogressively greater, so that the difference is compared with arespective upper threshold value which, when exceeded, indicates thatcatalytic converter 12 should be replaced.

Alternatively or additionally, the comparison may be based on theabsolute temperatures. This is illustrated in FIG. 2.

FIG. 2 shows the temperature of the exhaust gas emitted from catalyticconverter 12 plotted as a function of time. Up to a time t1, internalcombustion engine 1 is operated in stratified charge operation.Approximately at time t1 there is an additional injection followingcombustion. This additional injection and the resulting additionalconversion of the exhaust gases generated by catalytic converter 12result in an additional increase in temperature of the exhaust gas.

The additional temperature increase due to the additional injection isequivalent to a maximum temperature measured by temperature sensor 13and/or temperature sensor 14. This maximum temperature becomes smallerover time due to the aging of catalytic converter 12.

If catalytic converter 12 is not yet aged and if catalytic converter 12thus still has an adequate conversion capacity, this results in amaximum temperature which exceeds a lower threshold value 15. This isindicated with reference number 16 in FIG. 2.

However, if catalytic converter 12 no longer has an adequate conversioncapacity, then catalytic converter 12 is aged and is thus spent, so thatthreshold value 15 is no longer exceeded. This is labeled with referencenumber 17 in FIG. 2.

After time t2, internal combustion engine 1 is then again operated instratified charge operation by controller 18.

The method described above may be used continuously during operation ofinternal combustion engine 1. Alternatively or additionally, it ispossible to use this method specifically for diagnosing aging ofcatalytic converter 12.

What is claimed is:
 1. A method for diagnosing a catalytic converter ofan internal combustion engine of a motor vehicle, comprising the stepsof: injecting a fuel directly into a combustion chamber; burning thefuel during an intake phase in a first mode of operation and during acompression phase in a second mode of operation; sending an exhaust gasformed by combustion to the catalytic converter; injecting an additionalamount of the fuel following combustion in the second mode of operation;measuring a temperature of the exhaust gas at least one of in anddownstream from the catalytic converter; and comparing the temperatureof the exhaust gas with a threshold value; wherein a first temperatureincrease is measured and compared with a second temperature increasemeasured with one of a new catalytic converter and a defective catalyticconverter, and a difference between the first temperature increase andthe second temperature increase is compared with at least one of anupper limit value and a lower limit value.
 2. The method according toclaim, 1, wherein: the additional amount of the fuel is not ignited. 3.A storage medium that stores a computer program that when executed by acomputer enables a diagnosing of a catalytic converter of an internalcombustion engine of a motor vehicle to be performed in accordance witha method including: injecting a fuel directly into a combustion chamber;burning the fuel during an intake phase in a first mode of operation andduring a compression phase in a second mode of operation; sending anexhaust gas formed by combustion to the catalytic converter; injectingan additional amount of the fuel following combustion in the second modeof operation; measuring a temperature of the exhaust gas at least one ofin and downstream from the catalytic converter; and comparing thetemperature of the exhaust gas with a threshold value; wherein a firsttemperature increase is measured and compared with a second temperatureincrease measured with one of a new catalytic converter and a defectivecatalytic converter, and a difference between the first temperatureincrease and the second temperature increase is compared with at leastone of an upper limit value and a lower limit value.
 4. The storagemedium according to claim 3, wherein: the storage medium is a flashmemory.
 5. The storage medium according to claim 3, wherein: thecomputer is a microprocessor.
 6. A controller for diagnosing a catalyticconverter of an internal combustion engine of a motor vehicle,comprising: an arrangement for injecting a fuel directly into acombustion chamber; an arrangement for burning the fuel during an intakephase in a first mode of operation and during a compression phase in asecond mode of operation; an arrangement for sending an exhaust gasformed by combustion to the catalytic converter; an arrangement forinjecting an additional amount of the fuel following combustion in thesecond mode of operation; an arrangement for measuring a temperature ofthe exhaust gas at least one of in and downstream from the catalyticconverter; and an arrangement for comparing the temperature of theexhaust gas with a threshold value; wherein a first temperature increaseis measured and compared with a second temperature increase measuredwith one of a new catalytic converter and a defective catalyticconverter, and a difference between the first temperature increase andthe second temperature increase is compared with at least one of anupper limit value and a lower limit value.
 7. An internal combustionengine for a motor vehicle, comprising: a combustion chamber into whicha fuel is directly injected, the fuel being burned during an intakephase in a first mode of operation and during a compression phase in asecond mode of operation; a catalytic converter that receives an exhaustgas formed by combustion; and a controller for diagnosis of thecatalytic converter; wherein the controller causes an additional amountof the fuel to be injected following combustion in the second mode ofoperation, and the controller causes a temperature of the exhaust gas atleast one of in and downstream from the catalytic converter to bemeasured and compared with a threshold value; and wherein the controlleris configured so that a first temperature increase is measured andcompared with a second temperature increase measured with one of a newcatalytic converter and a defective catalytic converter, and adifference between the first temperature increase and the secondtemperature increase is compared with at least one of an upper limitvalue and a lower limit value.
 8. A method for diagnosing a catalyticconverter of an internal combustion engine of a motor vehicle.comprising the steps of: injecting a fuel directly into a combustionchamber; burning the fuel during an intake phase in a first mode ofoperation and during a compression phase in a second mode of operation;sending an exhaust gas formed by combustion to the catalytic converter;injecting an additional amount of the fuel following combustion in thesecond mode of operation; measuring a temperature of the exhaust gas atleast one of in and downstream from the catalytic converter; andcomparing the temperature of the exhaust gas with a threshold value;wherein a maximum temperature is measured and compared with a lowerthreshold value.
 9. A method for diagnosing a catalytic converter of aninternal combustion engine of a motor vehicle, comprising the steps of:injecting a fuel directly into a combustion chamber; burning the fuelduring an intake phase in a first mode of operation and during acompression phase in a second mode of operation; sending an exhaust gasformed by combustion to the catalytic converter: injecting an additionalamount of the fuel following combustion in the second mode of operation:measuring a temperature of the exhaust gas at least one of in anddownstream from the catalytic converter: and comparing the temperatureof the exhaust gas with a threshold value; wherein a temperatureincrease is measured and compared with a modeled temperature increase,and a difference between the temperature increase and the modeledtemperature increase is compared with an upper limit value.